The invention relates to a radial piston pump for high-pressure fuel supply in fuel injection systems of internal combustion engines, in particular in a common rail injection system. A drive shaft which is eccentrically supported in a pump housing and on which a ring is slidingly supported that cooperates with a plurality of pistons, disposed radially relative to the drive shaft in a respective cylinder chamber. The pistons are movable radially back and forth in the respective cylinder chamber by rotation of the drive shaft.
In one such radial piston pump, braced on the inside, the base of each of the pistons has contact with the ring supported on the drive shaft. Because of the eccentricity of the drive shaft, the pistons are successively set into a reciprocating motion. The stroke of the pistons is constant and corresponds to twice the amount of the eccentricity of the drive shaft.
To increase the efficiency of the engine, it has been proposed that the cylinder chambers be filled with less fuel as demand drops.
An object of the invention is to enable partial filling of the cylinder chambers of the radial piston pump. Wear of the individual components is to be minimized, and damage during operation is to be averted. In particular, the radial piston pump of the invention should withstand a pump pressure of up to 2000 bar in the feeding direction.
A radial piston pump for a high-pressure fuel supply in fuel injection systems of internal combustion engines, in particular in a common rail injection system, has drive shaft which is eccentrically supported in a pump housing and on which a ring is slidingly supported that cooperates with a plurality of pistons. The pistons are disposed radially relative to the drive shaft in a respective cylinder chamber. The pistons are movable radially back and forth in the respective cylinder chamber by rotation of the drive shaft, this object is attained in that a guide device prevents rotation of the ring its about its own axis. Within the context of the present invention, it has been found that the increased wear and damage in conventional radial piston pumps can be ascribed to rotation of the ring about its own axis. This rotation is prevented by the guide device.
One particular version of the invention is characterized in that the guide device has a protrusion, which extends at least partly parallel to the axis of rotation of the drive shaft and protrudes into an indentation whose dimensions are greater than those of the protrusion. The protrusion can be embodied either on the ring or on the pump housing. In the first case, the associated indentation is provided in the pump housing and in the second case it is provided in the ring. The protrusion can move in the transverse direction only as far as the dimensions of the indentation allow. This advantageously assures that the motions of the ring in the circumferential direction as limited.
A further special version of the invention is characterized in that the protrusion is embodied on the ring, and the indentation is embodied in the pump housing. The converse case is also possible, as noted above, but in that case the size of the indentation is limited to the dimensions of the ring. In the pump housing, conversely, adequate space for the indentation is available.
A further special version of the invention is characterized in that the protrusion and the indentation each take the form of a cylinder, whose longitudinal axis is parallel to the axis of the drive shaft. In the context of the present invention, it has been found that the ideal course of motion of the ring is a circle. It is accordingly advantageous if both the indentation and the protrusion are cylindrical. This reduces the motion of the ring in the circumferential direction to the minimum required by the eccentricity of the drive shaft.
A further special version of the invention is characterized in that the diameter of the indentation is equivalent to twice the sum of the eccentricity of the drive shaft and the radius of the protrusion. A circle with this diameter corresponds to the ideal guide path of the ring.
A further special version of the invention is characterized in that the diameter of the indentation is somewhat greater than twice the sum of the eccentricity of the drive shaft and the radius of the protrusion. This assures that the ring can move on its ideal path, without the protrusion and the indentation being in contact with one another. This has the advantage of reducing wear from friction. The protrusion does not come into contact with the indentation until the ring is no longer moving on its ideal path.
A further special version of the invention is characterized in that the protrusion is a pin, which is secured in a bore in the pump housing, and that the indentation is a bore. This is one of many variants for the design of the protrusion and the indentation. This variant has the advantage that it can be produced simply and economically. It furthermore allows the present invention to be applied to known radial piston pumps.
A further special version of the invention is characterized in that the indentation is embodied annularly. The protrusion protrudes into the annular indentation and can thus move only in the circumferential direction of the indentation. Consequently, the ring can execute only such motions as well. In this way, compulsory guidance of the ring along its ideal path of motion is advantageously assured.
A further special version of the invention is characterized in that the indentation is a bore in which a pin is secured. In this way, the annular shape of the indentation can be achieved simply and economically. Preferably, the diameter of the pin is somewhat less than twice the difference between the eccentricity and the radius of the protrusion.
A further special version of the invention is characterized in that radially to the drive shaft, at least three pistons are disposed, and on the end toward the drive shaft of each piston a plate is retained by a cage and is in contact with a flat face which is embodied on the ring. In a radial piston pump with a polygonal ring, the guide device of the invention has an especially advantageous effect. In experiments that have been performed with such a pump, it has been found that the ring can tilt about its axis if the cylinder chambers are not completely filled. This tilting is ascribed to the fact that in partial element filling, not all the plates rest permanently firmly enough on the ring. The tilting engenders impact forces on the plate that are transmitted to the cage and the piston. The resultant moments then cause damage to the affected components.
The guide device of the invention can in the simplest case comprise at least one guide piston, which in addition to the pistons already present is disposed radially to the drive shaft and rests on the ring.
Further advantages, characteristics and details of the invention will become apparent from the dependent claims and the ensuing description, in which one exemplary embodiment is described in detail in conjunction with the drawing. The characteristics recited in the claims and mentioned in the description can each be essential to the invention individually or in arbitrary combination. One way of embodying the claimed invention is described below in detail in conjunction with the drawing.